1. Field of the Invention
The present invention relates to blind channel searching and estimation using a fast Fourier transform (FFT) mechanism, and, more particularly, using an FFT-based mechanism during blind channel searching to effectively decrease the time required to complete a blind search. This method also guarantees that an exact signal in a DVB-S receiver is found.
2. Description of Related Art
A digital platform is mainly used in digital TV A digital platform is not just hardware, such as a set-top box or a TV, but also includes digital channels and digital content. High-quality digital content attracts viewers and encourages further development of digital content. Currently, global digital TV specifications are divided into two types: advanced television systems committee (ATSC) in the North America and digital video broadcasting (DVB) in Europe.
DVB systems are further separated into digital video broadcasting cable (DVB-C), digital video broadcasting satellite (DVB-S) and digital video broadcasting terrestrial (DVB-T). DVB-C is designed to meet the specifications for cable TV. DVB-S is designed to meet the specifications for satellite TV. DVB-T is designed to meet the specifications for terrestrial TV.
A local system provider can transmit signals, such as digital video broadcasting-S, to a user's satellite dish up to 22000 miles away via satellite. The transmission method uses quaternary phase shift keying (QPSK) to transmit MPEG-2 data.
A full blind channel search is necessary for a DVB-S receiver. A full blind channel search provides a sample operation mode without requiring a user to know program information. A full blind channel search automatically scans all programs. The search's speed is a key point for measuring a blind search algorithm and a fast search reduces waiting time.
The blind search method is based on back end software control of the prior art. A center frequency is set in a tuner. A filter bank and a timing recovery loop are started in the base band decoder chip. The base band decoder chip operates at a minimum symbol speed. If the timing recovery loop is unable to converge, the symbol speed is increased. A symbol speed in excess of a maximum value and lacking convergence indicates a lack of signal at a particular frequency point. When this occurs, a center frequency in the tuner is refreshed. A longer frequency is added to the original and the above steps are repeated until the timing recovery loop converges.
This method is disadvantageously slow. The symbol speed ranges from 1 Mbaud to 45 Mbaud and is very large. The channel of a satellite signal is width. The channel has 950 MHz-2150 MHz input ranges in a Ku tuner. The symbol speed and the channel of the satellite signal are the combination of many products. A blind search leads to longer search times for multiple combinations. Furthermore, to change the center frequency of tuner wastes a lot of time. The distance longer center frequency extends the search time and the timing recovery loop convergence will be very slow. The search symbol speed is slow when using the timing recovery loop.